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DS1302S+T&R

RTC with 31B RAM, 3-wire serial, trickle charger, 300nA backup, SOIC-16, 2-5.5V

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Manufacturer Part：

DS1302S+T&R

Package：

SOIC-16 Wide (10.50 x 7.60 x 2.35 mm)

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Integrated Circuits ICs

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Description

Product Overview

The DS1302S+T&R from Maxim Integrated (now Analog Devices) is a trickle-charge timekeeping chip with a real-time clock/calendar and 31 bytes of static RAM. Using a simple 3-wire serial interface, it operates from 2.0V to 5.5V with battery backup in a 16-pin SOIC package.

Key Specifications

Function	Real-Time Clock + 31B RAM
Interface	3-wire serial (CE, I/O, SCLK)
Clock Format	BCD: seconds, minutes, hours, day, date, month, year
12/24 Hour	Selectable
Supply Voltage	2.0 V to 5.5 V
Battery Backup	Yes (VCC1 pin, 2.0V min)
Trickle Charger	Programmable (1 or 2 diodes, 2k/4k/8k resistor)
Operating Current	300 nA typical (timekeeping, VCC1=2V)
Serial Clock Rate	Up to 2 MHz
Operating Temperature	-40°C to +85°C
Package	SOIC-16 (7.5mm wide)

Features

Real-time clock/calendar with BCD format and leap year compensation to 2100
31 bytes of battery-backed static RAM for non-volatile data storage
Programmable trickle charger for backup battery (supercap or rechargeable)
300nA timekeeping current for long battery life in backup mode
Simple 3-wire serial interface at up to 2MHz with burst mode

Applications

Time-stamping in data loggers and industrial controllers
Embedded system time-of-day reference with battery backup
Utility metering and point-of-sale terminal timekeeping

Product Introduction:DS1302S+T&R Product Introduction

The DS1302S+T&R from Maxim Integrated (now Analog Devices) is a trickle-charge timekeeping chip containing a real-time clock/calendar and 31 bytes of static RAM. It communicates with a microprocessor via a simple 3-wire serial interface (CE, I/O, SCLK). The real-time clock provides seconds, minutes, hours, day, date, month, and year information, with automatic leap year compensation valid up to 2100. The clock operates in either 24-hour or 12-hour format with AM/PM indication. The 31 bytes of RAM can be used for storing configuration data or time-stamp information that survives power loss when backed up by battery. A programmable trickle charge circuit allows direct charging of a backup supercapacitor or rechargeable battery from the primary supply. The DS1302 operates from 2.0V to 5.5V and consumes only 300nA in timekeeping mode, ensuring years of backup life from a small battery or supercapacitor.

Working Principle:DS1302S+T&R Working Principle

The DS1302S+T&R operates as a serial-interfaced real-time clock with battery backup. (1) Timekeeping: An external 32.768kHz crystal provides the timebase. The internal oscillator divides the crystal frequency to generate 1Hz ticks for the seconds counter. The BCD counters cascade through seconds, minutes, hours, day, date, month, and year. (2) 3-Wire Interface: Communication requires three signals: CE (chip enable), I/O (bidirectional data), and SCLK (serial clock). Read and write operations are initiated by an 8-bit command byte (7-bit address + 1-bit R/W), followed by 8 bits of data. Burst mode reads or writes all 31 RAM bytes plus clock registers sequentially. (3) Dual Supply: VCC2 is the primary supply and VCC1 is the backup. When VCC2 > VCC1 + 0.2V, the device is powered from VCC2. When VCC2 falls below VCC1, the device switches to battery backup from VCC1, maintaining timekeeping at 300nA. (4) Trickle Charger: A programmable charge path connects VCC2 to VCC1 through a series combination of 1 or 2 diodes (for voltage drop) and a 2k/4k/8k resistor (for current limiting), allowing controlled charging of the backup battery.

Pin Description:DS1302S+T&R Pin Definition and Functions

Pin	Name	Function
1	VCC1	Backup supply (battery)
2,3	X1, X2	32.768kHz crystal
4	GND	Ground
5	CE	Chip enable (active high)
6	I/O	Bidirectional data
7	SCLK	Serial clock input
8	VCC2	Primary supply (2-5.5V)